Boötes the Herdsman is a Northern Hemisphere constellation best seen in the late spring or early summer. And it’s one of the largest constellations in the sky, ranking 13th out of 88. Boötes is most famous for its bright star Arcturus, which is the 4th-brightest star in the night sky.
Locating the constellation Boötes
You can find Boötes south of Ursa Major the Great Bear, off the handle of the Big Dipper. Boötes’ brightest star, Arcturus, is part of a mnemonic device used to orient people to the night sky. As the saying goes, Arc to Arcturus, speed on to Spica. This means that as you follow the curve in the Dipper’s handle away from Ursa Major, you will run into a bright star: Arcturus in Boötes. Then continue the curve along and you’ll find Spica, which is a part of Virgo.
Tracing out the shape of Boötes
Boötes is supposed to be the figure of a man, which is somewhat recognizable with its tall diamond shape and two stick legs jutting out at the bottom.
And the point at which the tall diamond shape and stick legs intersect is the star Arcturus. In addition, the Herdsman also appears to have his left arm raised over his head. Some say it’s easy to pick out as a kite-shaped group of stars.
The stars in the Herdsman
Arcturus, the brightest star in Boötes, shines at magnitude -0.04, making it the 4th-brightest star in the night sky.
The name Arcturus means bear watcher or bear guard, referring to its closeness to the Great Bear, Ursa Major. Lying 37 light-years away from Earth, Arcturus glows with a faint orange hue.
The 2nd brightest star in Boötes lies on the left side of the diamond shape. It’s called Izar, or Epsilon Boötis, and is 10 degrees up from Arcturus. It’s a magnitude 2.37 star lying 203 light-years away.
And the 3rd brightest star in Boötes is his left knee, which is found to the lower right of Arcturus. This star is Muphrid, or Eta Boötis, at magnitude 2.68. Muphrid lies 37 light-years away.
Fainter stars in Boötes
The other stars in the body of the Herdsman are all of comparable brightness. Starting above Izar and working up, around and back toward Arcturus are the stars Delta Boötis, Beta Boötis aka Nekkar (consider this Boötes’ neck), Gamma Boötis (or Seginus) and Rho Boötis.
Delta Boötis shines at magnitude 3.46 at a distance of 121 light-years. Nekkar shines at magnitude 3.49 and lies 219 light-years distant. Seginus has the brightest magnitude of these four stars, at 3.04. It is also the closest of the four at 84 light-years. Finally, Rho Boötis, which lies almost even with Izar, shines at magnitude 3.57 and lies 149 light-years away.
Arcturus shows large proper motion
The bright orange star Arcturus is especially noteworthy for its large proper motion, or sideways motion as seen on the dome of Earth’s sky.
Indeed, Arcturus is actually moving at a tremendous speed (122 km/s or 76 miles/s) relative to our solar system. And from the vantage point of Earth, Arcturus is rapidly moving in a southerly direction at a rate of 3.9 arcminutes per century.
Its closest point to Earth will be about 4,000 years from now. Then as it moves away, it will vanish from visibility to the unaided eye in about 500,000 years.
So why does it move so much faster than the other stars in Boötes? It’s because Arcturus is much closer to us than the constellation’s other stars. And that’s also why it’s so much brighter than its companions.
Constellation Boötes proper motion from 30k years ago to 30k years from now. pic.twitter.com/tXHd7cFdFc
— Tony Dunn (@tony873004) June 16, 2022
Spotting Boötes in the Southern Hemisphere
Via Daniel Gaussen, Founder & Guide – Stargaze Mackenzie – New Zealand
Although Boötes is a northern constellation, it is still visible from much of the Southern Hemisphere, including New Zealand. The constellation culminates in the northern sky during the evenings of late autumn and early winter.
Boötes sits low above the northern horizon from Southern Hemisphere latitudes, so its distinctive kite-shaped outline can be harder to pick out than it is for northern observers. Plus it also appears inverted compared with Northern Hemisphere star charts, conveniently placing bright Arcturus above the rest of the pattern rather than below it.
As a result, Arcturus stands out immediately among the fainter stars of Boötes and is easily the brightest star in the northern sky, acting as a clear anchor for locating the constellation from the Southern Hemisphere. Reaching about 30 degrees above the northern horizon from New Zealand, it remains a striking orange beacon despite its low altitude.
Over vast timescales, Arcturus’ proper motion will carry it further south, one day placing this brilliant star far higher in southern skies than it appears today, while Boötes itself remains essentially unchanged to the naked eye for countless generations.
Bottom line: Boötes the Herdsman is a large constellation that holds one of the brightest stars in the sky, Arcturus.
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